Vintage Sears Silvertone radio safety question

[usradcoll1]

Originally Posted by merlinmaxwell

Enough for the radio though.
A pound seems OK for that sort of thing. If plugged in and it hums a bit and gets slightly warm after an hour or so then it is a proper job.

The radio is about 30/35 watts @ 120volts. It should be OK.

[sweepthedog]

I've put a thread in the repair part of the website, hopefully someone replies soon, it would so nice to get it working!

[sweepthedog]

Final update, new bulb and no light. Oops.
I pray to God it isnt the valve heaters

[Gabe001]

Originally Posted by sweepthedog

Final update, new bulb and no light. Oops.
I pray to God it isnt the valve heaters

If it's just one of the valve heaters, you just unplug the valve and put a replacement in. The valves seem available and not too pricey

For example (no affiliation with seller)
https://www.ebay.co.uk/itm/35z4gt-CV....m46890.l49286

It's a really beautiful set, I hope you find someone to look at it for you.

Gabriel

[sweepthedog]

what is the different between a vacuum tube and a valve heater? It has 5 things in it which look like that competent you linked on ebay but different shapes and sizes (like in the pic I attached ) one is dated Feb 1939 so I would deffo like that to remain(middle one with brown paper on it)

Thank you it really is, I wish art deco would make a comeback !

[Station X]

The five items along the back of the set are vacuum tubes, commonly referred to as valves in the UK.

Each valve contains a heater, the part which should light up.

[newlite4]

The heater chain really is just like a set of Christmas tree lights but with a resistor at one end. What you need to do is to carefully remove each valve in turn and test between pins 2 and 7. Using an ohmmeter on the X1 range just check for continuity to establish that each heater is intact.
Neil

[sweepthedog]

Hi Guys

Chris (unitelex) is repairing the radio and luckily the only thing burnt out is one valve.
The valve is a 12Q7GT which has a 12V 150mA heater .

There are a few British NOS on eBay but I was wondering and it's a long shot if anyone has or knows where to acquire a Sears Silvertone Valve of the same spec? Just for authenticity purposes.

Cheers

[usradcoll1]

Originally Posted by sweepthedog

Hi Guys

Chris is repairing the radio and luckily the only thing burnt out is one Valve.
The valve is a 12Q7GT which has a 12V 150mA heater .

There are a few british NOS on ebay but I was wondering and its a long shot if anyone has or knows where to acquire a Sears Silvertone Valve of the same spec? Just for authenticity purposes

Cheers

Per the picture you posted, the radio has a valve that has been replaced by a substitute valve, the convertor or frequency changer. The socket has been rewired for a 12SA7, which is a metal, single ended valve, an electrical equivalent 12A8GT, that was originally supplied. The 12SA7 is a US Army surplus issue probably RCA sourced.
Dave, USradcoll1

[G8UWM-MildMartin]

I appreciate that you'd like an original Silvertone 12Q7GT "tube" but they were only sold in the USA. One may crop up on Ebay.com occasionally if you keep a watch, but the postage will not be cheap! (Sears/ Silvertone didn't make them, just put their name on, anyway)

BRIMAR (BRItish Made American Range), Ferranti, Tungsram (and probably others I've forgotten) made (or imported) valves especially as replacements for any American ones in sets in use in the UK.
Since the original brand was never sold here and they did sometimes fail, no-one would know that it wasn't an authentic 1940s-1950s repair for any other make then available in the UK to be used as a replacement.

[usradcoll1]

Originally Posted by G8UWM-MildMartin

I appreciate that you'd like an original Silvertone 12Q7GT "tube" but they were only sold in the USA. One may crop up on Ebay.com occasionally if you keep a watch, but the postage will not be cheap! (Sears/ Silvertone didn't make them, just put their name on, anyway)

BRIMAR (BRItish Made American Range), Ferranti, Tungsram (and probably others I've forgotten) made (or imported) valves especially as replacements for any American ones in sets in use in the UK.
Since the original brand was never sold here and they did sometimes fail, no-one would know that it wasn't an authentic 1940s-1950s repair for any other make then available in the UK to be used as a replacement.

The Sears/Silvertone valves were, either OEM or purchased at a Sears store or though the Sears catalogue. It possibly was repaired at a Sears repair center, as it appears that the 35Z4/5 was replaced early in the life of the radio.
BTW, that radio was built by Detrola, a firm that went out of business in the late 40's.
Dave, USradcoll1 A bit of trivia for today!

[sweepthedog]

Thanks Dave and everyone else
It really is interesting to learn about the history of it, me and my partner cant get over war broadcasts would have gone through it in '39!

Another question to show my ignorance what do the numbers on the tuner mean? They arent in ascending order like one would expect on a tuning scale liek on modern am/fm sets?

Thanks

[usradcoll1]

The scale is calibrated in KC, less the last "0". The common US broadcast band, 550 to 1600kc. The modest priced radios at the time had direct drive tuning indicators. The US, like other places in the world, was just coming out of the depression and many couldn't spend too much on a radio.
Dave, USradcoll1, still interested!

[unitelex]

Hello all, an update on progress with this set.
As per post #48, the 12Q7GT Detector-AF heater was O/C. Replaced it with a NOS Brimar 12Q7GT.
The set then powered up, all heaters and the lamp from a 120V DC supply, 200mA drawn ~24W.
DC voltages agreed with the data sheet give or take a little.
Some faint signals could be tuned and heard albeit at low volume level (volume pot at max). No external antenna or earth is connected at this point.
I aligned the IF and the Osc/Antenna trimmers (were all slightly out of tune)
I could not quite reach 1720 KHz as per the oscillator alignment instruction, maybe L2 needs some adjustment. Will get to that later, the threaded core is soldered to the chassis.
As pointed out by USradcoll1, this set has a different 1st stage frequency converter valve 12SA7 metal can no top cap, the schematic indicates 12A8GT glass with top cap.
Also the circuit around this stage is not as per the schematic, rather it more closely follows the schematic in the link below. It uses the centre tapped oscillator coil:
https://www.radiomuseum.org/tubes/tube_12sa7.html

It responds well and can be tuned to a modulated carrier from my Sig. Gen. driven into a loop of wire, and the volume is relatively loud.

Testing so far has been in my basement workshop and off-air signals are very weak down here - so not really fair to it. I will try it at ground floor level. maybe outdoors away from digital interference and with an external antenna / earth.

Chris


.

[usradcoll1]

It's great that the only items that were damaged was the dial lamp and the 12Q7GT valve. I thought for sure that the 50 ohm dropper resistor would be as well!
I thought that the osc coil with the adjustment screw being soldered to the chassis. A bit of a bodge!
Dave, USradcoll1 The OP sent it to the best tech.

[unitelex]

Having now tested reception in my garden I can confirm many stations are received.
Inside the house I could only really get R5 live, plus lots of buzzing interference from computers and various switched-mode converters. My Ravpower 3 port USB charger seemed the worst offender, although it was admittedly quite close - this obliterated the band.

A second test of the Silvertone at my parents house (larger garden, fields on 2 sides) showed at least 10 stations could be received loud and clear without external antenna with more coming in with a short wire antenna, no buzzing at all in this location.
My conclusion:
Nice compact and thermally efficient short superhet set, -best suited for rural areas /low tech households. Needs a conventional iron step down transformer to 110v

[Gabe001]

The OP must be very pleased.

He will be asking you for an AM pantry transmitter next!

[sweepthedog]

I am pleased! The videos Chris has sent are amazing and it certainly looks the part! I cant wait to see what it can get in York

I have bought another British made and more reliable 'autotransformer' off amazon:

https://www.amazon.co.uk/gp/product/...?ie=UTF8&psc=1

It converts voltage but not frequency (Hz). I assume this radios will still run well on 50Hz despite being made for 60hz?

I have been watching repairs from the US and they mention how it can have a 'hot' chassis (and unpolarised plug) and the set is not earthed. For everyday safety would you use a 'plug in' RCD to use before the transformer to ensure the safety in lieu of an earth?
I am not sure if I understand it right I just want it to be as safe as I can.


Cheers!

[Gabe001]

I'm sure Chris would have made sure neutral is connected to chassis. Does it not have a 3 pin plug to make sure it's always connected in the same way?

If you want to be safer you can use an RCD, although if your house has one already, as has been standard for decades, I'm not sure it would benefit you additionally.

I don't see the 50hz making a dramatic difference. It may affect HT smoothing in that you may drop a few volts due to the longer capacitor discharge cycle, but it's likely you won't notice any difference.

Happy to be corrected if wrong

[sweepthedog]

Thank you. The plug is the original American one 2 pin and can go in either way.